From the Metronet Alliance announcement (19 may 2008):
"On the 16 June, 2008, the final acceptance and sign-off by London Underground of Hydrotech’s technology is due to occur, which will allow its widespread use within the UK underground rail sector, subject to cost considerations."
I'm not sure if they'll be announcing that pen has been put to paper or if this is enough... but I'm happy as long as they keep suring up contracts.